test: Do SynchronousDelete cleanup before testing ImageIsUnpacked
test: Do SynchronousDelete cleanup before testing ImageIsUnpacked

Simply delete the image will not clean up the snapshots.

Signed-off-by: Li Yuxuan <2e5c14b5ad9ff06e0374b6360d5a43be80d19be5@baidu.com>

mikebrow/containerd,estesp/containerd,crosbymichael/containerd,containerd/containerd,containerd/containerd,vdemeester/containerd,thaJeztah/containerd,crosbymichael/containerd,thaJeztah/containerd,vdemeester/containerd,dmcgowan/containerd,mikebrow/containerd,dmcgowan/containerd,estesp/containerd